1. Field of the Invention
The present invention relates to a fluid filled elastomeric damping device which is used as a power unit mounting to a vehicle body or the like.
2. Description of the Prior Art
An example of a prior art power unit mounting, as is disclosed in Japanese Utility Model Provisional Publication No. 62-91037, includes two fluid chambers, an orifice for providing communication between the fluid chambers, a diaphragm partly defining one of the fluid chambers and a diaphragm restraining mechanism for selectively restraining and freeing movement of the diaphragm and thereby enabling the power unit mounting to have two different resonance frequencies or operational characteristics. In this instance, the power unit mounting has a damping or oscillatory system a mass and spring of which are constituted by the fluid within the orifice and the resilient walls enclosing the fluid chambers, i.e., the resilience in expansion and contraction of the fluid chambers, respectively. The resonance frequency can therefore be varied by varying the mass and/or spring, and in case of the above prior art mounting the different resonance frequencies or operational characteristics are obtained by varying the resilience in expansion and contraction of the fluid chambers.
A problem of the prior art power unit mounting is that the diaphragm in a state of being restrained in movement is liable to move in response to a variation of the pressure in the associated fluid chamber, making it imposible to attain a desired damping action at the time of restraint of the diaphragm.